The present invention relates to new compositions of matter having antibacterial properties, namely Fortimicin KG.sub.1, Fortimicin KG.sub.2 and Fortimicin KG.sub.3. The invention also pertains to the production of Fortimicin KG.sub.1, Fortimicin KG.sub.2 and Fortimicin KG.sub.3 by culturing a microorganism belonging to the genus Micromonospora, which is capable of producing at least one of the active substances in a nutrient medium, until antibacterial activity is detected in the culture liquor and then isolating at least one of the active substances therefrom.
Antibiotics which exhibit activity against a broad spectrum of bacteria are always in demand. To this end, it has been found that when certain strains of Micromonospora are cultured in a nutrient medium, several antibiotic substances are produced in the culture liquor. Specifically, Fortimicin factors A, B, C, D, KE, KF and KG have been isolated from the culture liquor of Micromonospora olivoasterospora MK-70 (ATCC 21819) (FERM-P No. 1560) and have the following structural formulae: ##STR1##
The chemical, physical and biological properties of these antibiotics and the processes for the production thereof are explained in detail in the specifications of the aforementioned United States Patents and Patent applications.
It has now been found that Micromonospora olivoasterospora MK-70, when cultured, liberates three further active substances. A study of the chemical, physical and biological properties of these active substances indicates that the compositions of matter are new antibiotics which have now been named Fortimicin KG.sub.1, Fortimicin KG.sub.2 and Fortimicin KG.sub.3.